1. Field of Invention
This invention relates to constant speed stroke-write vector display systems, and more particularly to a stroke-writer system having horizontal and vertical deflection signal pre-starts to eliminate displayed stroke vector distortion due to deflection signal noise.
2. Description of the Prior Art
As may be known, the stroke-write method of displaying information on a cathode ray tube (CRT) include the use of a series of stroke vectors connected by interim wait periods to generate a video data display, such as mapping data or alpha-numeric characater generation. Such systems operate at high writing speeds, requiring rapid changes in the horizontal and vertical deflection signals to permit the required rapid change in vector magnitude and deflection angle (directional displacement). At the beginning of each stroke vector display time, the deflection signals are maintained at a constant value to hold the CRT electron beam stationary for a "waiting" period, to permit the electron beam to settle. The deflection signals for the displayed stroke vector are then generated at a rate magnitude which is a function of the stroke vector deflection angle, corresponding to the desired directional displacement of the new vector. The rapid start up of the deflection signals at relatively high switching frequencies causes "ringing" noise at the initialization of the deflection sweep voltages, resulting in a characteristic "hook distortion" on the leading edge of the displayed stroke vector. Such distortion is undesirable since it results in a loss in fidelity of the displayed data.
Due to the wide variation in stroke vector magnitudes and deflection angles, from 0.degree. to 360.degree. , elimination of the displayed vector distortion by use of prior art methods of: (1) providing a fixed threshold voltage above the deflection signal noise level on both the horizontal and vertical deflection channels which requires both deflection signals to exceed the threshold before video display of the stroke vector is permitted, or (2) delaying the video display for a fixed time interval following the start of the deflation signals, are impractical. In (1)the variations in the magnitude of the non-displayed portion of the stroke vector resulting from the wide variation in vector deflection angles creates substantial errors in the displayed magnitude of the stroke vector, and in (2) there is a failure to display the full stroke vector magnitude.